South Sudan's SPLA-In Opposition rebels have denied attacking Malakal town in Upper Nile state as fighting continued there for a second day.

SPLA-IO spokesperson Dickson Gatluak claimed in a press statement that government forces attacked them at Doleib Hill, an area outside the town, but were defeated.

Fighting broke out in Malakal town last night between government troops and forces under command of Major General Johnson Olony. Today government spokesperson Michael Makuei Lueth had said the rebels attacked Malakal itself last night assisted by Olony, AFP reported.

"The rebels of Riek Machar have attacked Malakal from all directions, from east, west, north, and south, and the fighting up to now is continuing," Makuei said, saying the rebels crossed the Nile which lies to the west.

Olony, a commander of a Shilluk armed group who previously rebelled against the government, had remained loyal to Juba throughout the South Sudan Civil War. His men have been stationed on the west bank of the Nile and clashed with other SPLA forces in Malakal last month.

The Intergovernmental Authority on Development, which monitors ceasefire violations, released a preliminary report today accusing a combined force of Olony's men and the SPLA-IO of attacking Malakal.

"Shilluk militia forces of General Johnson Olony joined by forces from the SPLM/ SPLA-IO attacked against Government forces in and around Malakal," IGAD said in a statement, though did not name the commanding officers of either the government or SPLA-IO forces involved.

Gatluak, the SPLA-IO rebel spokesperson, refuted this claim. "It is clear to everyone on the ground that the government is the one attacking us at the west bank of Nile River and in the causes of the fighting, both rival forces ending up in the town," he said.

IGAD said it is "deeply frustrated by the spread of violence to Upper Nile and strongly condemns this serious violation of the Cessation of Hostilities Agreement by SPLM/SPLA-IO and its allied forces and urge the warring Parties to immediately end the killings and all hostilities ravaging the country."

It is unclear which side of the SPLA - the government, Olony's forces, SPLA-IO, or a mix of the three - currently holds Malakal town.

Upper Nile state government officials were unable to say which armed group of the SPLA controlled the riverside capital, but said they were dislodged and are taking refuge in Akoka county and other areas. Gatluak asserted that Olony was in complete control. Radio Tamazuj was unable to reach Olony's side.